This invention relates to an apparatus for embossing modulated grooves on a carrier medium as a function of received electronic signals and, more particularly, to such an apparatus wherein the electronic signals may represent video information. The subject matter of this application is related to subject matter disclosed in the copending U.S. application Ser. No. 517,530 of James White entitled "Apparatus For Embossing Information On a Disc" now U.S. Pat. No. 3,946,149.
There have been recently developed a number of systems for storing video and audio information on a carrier medium which, ideally, could be purchased by consumers at a reasonable cost and reproduced in conjunction with their conventional home television receivers. Typically, the consumer would purchase a "player" which would recover electronic video signals from a recording medium and these signals would be applied to the antenna terminals of a television set for display. There has been widespread disagreement as to what type of recording medium provides the maximum overall advantage of cost, performance, and reliability, with systems using magnetic tape, film and discs similar to long playing records, all receiving support from different technical factions. During the last five years it has been demonstrated that video discs, which are in some respect similar to conventional sound recording discs, are capable of producing reasonable quality picture information. It is generally thought that these discs, which can be pressed from vinyl in a manner similar to conventional audio disc pressing, offer a great advantage of economy to the consumer, but disc systems present a number of new technical problems when it is attempted to record the relatively high frequencies required for video information thereon. For example, it is necessary that the video disc store about one hundred times the capacity of information of an audio record, and that the video disc reproducer handle a flow of information that is of the order of one hundred times faster than a photograph pickup. Accordingly, the undulations in the disc grooves are much smaller than those of a conventional audio record and the necessarily small dimensions lead to problems in making the discs and in playback. Various types of playback systems have been proposed, for example playback employing an electrostatic capacitive-discharge technique or playback employing a pressure-type transducer which "slides" over the record grooves. In most systems, however, there is a common problem in producing the discs and, more specifically, in fabricating master discs from which relatively high quality duplicates can be pressed.
There are two types of "master" fabrication techniques that are of interest herein; i.e., electron beam processes and mechanical cutting processes. In the electron beam process a carrier is coated with an electron-sensitive material and selectively exposed using a modulated electron beam. This type of recording has been performed successfully, although electron beam recording is a relatively expensive technique which requires a strigently controlled environment. Also, there has been difficulty in achieving electron beam recording in "real time" since at video frequencies this would require the beam to expose the electron-sensitive material at a high rate of relative motion which limits the amount of exposure time for each elemental area of electron-sensitive material and aggravates tracking problems. Therefore, it is the present practice to record using an electron beam at about one twentieth of real time, which is typically achieved by reducing the frequency of input signals by a factor of 20 and slowing the relative motion between the beam and the carrier by the same factor of 20.
The mechanical cutting process has also apparently been performed with some success. A company which is introducing a commercial video disc system claims to make masters using a mechanical cutting process similar to that used for conventional records. However, they acknowledge that the mechanical cutting process is not performed in real time, which is not surprising since conventional cutters cannot be satisfactorily operated at the megahertz frequencies necessary for real time recording.
It is accordingly one object of the present invention to provide an improved technique of mechanically embossing relatively high frequency information on a record medium, the embossing being capable of being done in real time.